1. Field of the Invention
The invention relates to pumping molten metal and more particularly to an impeller and shaft suited for use in a molten metal pump.
2. Brief Description of Prior Art
A molten metal pump apparatus generally includes a motor mounted above a molten metal bath. The motor drives a rotatable impeller pump having one or more impellers submerged in the bath. In operation, the rotating impellers draw molten material from the bath and pump it through a conduit routed to a subsequent station for further processing.
The molten metal pump typically includes a base having inlet and outlet passages for intake and discharge of the molten metal being pumped. The pump base together with the impeller are submerged in the molten metal by means of posts. The impeller is supported for rotation by means of a rotatable shaft connected to the drive motor located atop a platform which is also supported by the posts.
The portions of the pump assembly submerged in the molten metal are directly contacted and exposed to the harsh conditions thereof, and are formed of refractory material such as graphite, silicone carbide, alumina, zirconia or hexalloy. The posts extend through a level of the molten metal and are connected to a motor mounting plate of the drive arrangement positioned above the level molten metal.
In addition to the hostile environment at the interface between the molten metal and atmosphere, even the molten metal bath itself is not homogeneous. That is, certain suspended solids can be present including unmelted chunks of scrap metal, chunks of alloying metals, and contaminants such as refractory brick spalled from the wall of the furnace, chunks of cement, insoluble metal oxide accretions and the like.
In attempts to eliminate or minimize such problems in the past, immersed impellers of the pumps are either a cup shaped centrifugal impeller having plural radial or angularly directed radial passages with a hollow center portion receiving the molten metal from the inlet and, by centrifugal action, directing the molten metal out the angular radial passages or, a vaned impeller having a generally disc shaped web with flat surface or curved outwardly radially extending vanes.
The impeller is also provided with a base section which serves as the connecting section with the drive shaft and the number of vanes extend approximately radially from the base section. In the prior art, the vanes are not connected to the shaft, and is known as the open-type vanes. In the prior art, the impeller generally includes a central hub for appropriately attaching the shaft thereto and further includes the radially directed vanes as previously described. Generally, the connection between the shaft and impeller has been by male threading on the shaft engaging female threading in the central hub of the impeller with a distinct shoulder at the junction. Potential problems upon attempted replacement of the shaft or the impeller are encountered similar to the replacement problems with respect to the support posts. That is, careful, difficult, labor-intensive manual hammer and chisel work is required to remove all of the old pieces.
Accordingly, an impeller having low clogging characteristics, yet also providing high efficiencies would be highly desirable in the art. The current invention achieves these objectives. Moreover, the current invention achieves a number of advantages in directional forced metal flow. For example, the impeller of the current pump is not prone to clogging as in many of the prior impellers. Accordingly, catastrophic failure is much less likely to occur and the effectiveness of operation does not degrade rapidly over time. The design also achieves high strength between the impeller and shaft and further increases the load area via a contiguous top surface. Furthermore, the impeller and shaft design can be prepared with relatively simple manufacturing processes. Therefore, the cost of production is low and accommodates a wide selection of materials, such as graphite or ceramics.
As will be seen from the subsequent description, the preferred embodiments of the present invention overcome shortcomings of the prior art.